Added requirement for pip>=1.3

This should upgrade pip on Jenkins to a version that removes the "build" directory, which should solve the issues we've been having with version conflicts between packages.

I verified that it upgrades pip by running the manual test branch Jenkins job, then checking the version of pip in that virtualenv.

@brianhw Reviewed before the git history rewrite.  (Brian, after some testing I determined that pip requirements are not installed in line order, so I moved the pip line back into its alphabetical position)

@nedbat Please review